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Sun F, Indran IR, Zhang ZW, Tan MHE, Li Y, Lim ZLR, Hua R, Yang C, Soon FF, Li J, Xu HE, Cheung E, Yong EL. A novel prostate cancer therapeutic strategy using icaritin-activated arylhydrocarbon-receptor to co-target androgen receptor and its splice variants. Carcinogenesis 2015; 36:757-68. [PMID: 25908644 DOI: 10.1093/carcin/bgv040] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 03/18/2015] [Indexed: 11/13/2022] Open
Abstract
Persistent androgen receptor (AR) signaling is the key driving force behind progression and development of castration-resistant prostate cancer (CRPC). In many patients, AR COOH-terminal truncated splice variants (ARvs) play a critical role in contributing to the resistance against androgen depletion therapy. Unfortunately, clinically used antiandrogens like bicalutamide (BIC) and enzalutamide (MDV), which target the ligand binding domain, have failed to suppress these AR variants. Here, we report for the first time that a natural prenylflavonoid, icaritin (ICT), can co-target both persistent AR and ARvs. ICT was found to inhibit transcription of key AR-regulated genes, such as KLK3 [prostate-specific antigen (PSA)] and ARvs-regulated genes, such as UBE2C and induce apoptosis in AR-positive prostate cancer (PC) cells. Mechanistically, ICT promoted the degradation of both AR and ARvs by binding to arylhydrocarbon-receptor (AhR) to mediate ubiquitin-proteasomal degradation. Therefore, ICT impaired AR transactivation in PC cells. Knockdown of AhR gene restored AR stability and partially prevented ICT-induced growth suppression. In clinically relevant murine models orthotopically implanted with androgen-sensitive and CRPC cells, ICT was able to target AR and ARvs, to inhibit AR signaling and tumor growth with no apparent toxicity. Our results provide a mechanistic framework for the development of ICT, as a novel lead compound for AR-positive PC therapeutics, especially for those bearing AR splice variants.
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Affiliation(s)
- Feng Sun
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Inthrani R Indran
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Zhi Wei Zhang
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - M H Eileen Tan
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Yu Li
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Z L Ryan Lim
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Rui Hua
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Chong Yang
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore, Cancer Biology and Pharmacology, Genome Institute of Singapore, Agency for Science, Technology and Research, 138672 Singapore, Singapore and
| | - Fen-Fen Soon
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - Jun Li
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore
| | - H Eric Xu
- Laboratory of Structural Sciences, Center for Structural Biology and Drug Discovery, Van Andel Research Institute, 333 Bostwick Avenue, N.E., Grand Rapids, MI 49503, USA
| | - Edwin Cheung
- Cancer Biology and Pharmacology, Genome Institute of Singapore, Agency for Science, Technology and Research, 138672 Singapore, Singapore and
| | - Eu-Leong Yong
- Department of Obstetrics and Gynecology, Yong Loo Lin School of Medicine, National University of Singapore, 119074 Singapore, Singapore,
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Sasi NK, Tiwari K, Soon FF, Bonte D, Wang T, Melcher K, Xu HE, Weinreich M. The potent Cdc7-Dbf4 (DDK) kinase inhibitor XL413 has limited activity in many cancer cell lines and discovery of potential new DDK inhibitor scaffolds. PLoS One 2014; 9:e113300. [PMID: 25412417 PMCID: PMC4239038 DOI: 10.1371/journal.pone.0113300] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 10/23/2014] [Indexed: 12/16/2022] Open
Abstract
Cdc7-Dbf4 kinase or DDK (Dbf4-dependent kinase) is required to initiate DNA replication by phosphorylating and activating the replicative Mcm2-7 DNA helicase. DDK is overexpressed in many tumor cells and is an emerging chemotherapeutic target since DDK inhibition causes apoptosis of diverse cancer cell types but not of normal cells. PHA-767491 and XL413 are among a number of potent DDK inhibitors with low nanomolar IC50 values against the purified kinase. Although XL413 is highly selective for DDK, its activity has not been extensively characterized on cell lines. We measured anti-proliferative and apoptotic effects of XL413 on a panel of tumor cell lines compared to PHA-767491, whose activity is well characterized. Both compounds were effective biochemical DDK inhibitors but surprisingly, their activities in cell lines were highly divergent. Unlike PHA-767491, XL413 had significant anti-proliferative activity against only one of the ten cell lines tested. Since XL413 did not effectively inhibit DDK in multiple cell lines, this compound likely has limited bioavailability. To identify potential leads for additional DDK inhibitors, we also tested the cross-reactivity of ∼400 known kinase inhibitors against DDK using a DDK thermal stability shift assay (TSA). We identified 11 compounds that significantly stabilized DDK. Several inhibited DDK with comparable potency to PHA-767491, including Chk1 and PKR kinase inhibitors, but had divergent chemical scaffolds from known DDK inhibitors. Taken together, these data show that several well-known kinase inhibitors cross-react with DDK and also highlight the opportunity to design additional specific, biologically active DDK inhibitors for use as chemotherapeutic agents.
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Affiliation(s)
- Nanda Kumar Sasi
- Laboratory of Genome Integrity and Tumorigenesis, Van Andel Research Institute (VARI), Grand Rapids, MI, United States of America
- Graduate Program in Genetics, Michigan State University, East Lansing, MI, United States of America
| | - Kanchan Tiwari
- Laboratory of Genome Integrity and Tumorigenesis, Van Andel Research Institute (VARI), Grand Rapids, MI, United States of America
| | - Fen-Fen Soon
- Laboratory of Structural Sciences, VARI, Grand Rapids, MI, United States of America
| | - Dorine Bonte
- Laboratory of Genome Integrity and Tumorigenesis, Van Andel Research Institute (VARI), Grand Rapids, MI, United States of America
| | - Tong Wang
- Translational Drug Development, Inc. (TD2), Scottsdale, AZ, United States of America
| | - Karsten Melcher
- Laboratory of Structural Biology and Biochemistry, VARI, Grand Rapids, MI, United States of America
| | - H. Eric Xu
- Laboratory of Structural Sciences, VARI, Grand Rapids, MI, United States of America
| | - Michael Weinreich
- Laboratory of Genome Integrity and Tumorigenesis, Van Andel Research Institute (VARI), Grand Rapids, MI, United States of America
- * E-mail:
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Tan MHE, Zhou XE, Soon FF, Li X, Li J, Yong EL, Melcher K, Xu HE. The crystal structure of the orphan nuclear receptor NR2E3/PNR ligand binding domain reveals a dimeric auto-repressed conformation. PLoS One 2013; 8:e74359. [PMID: 24069298 PMCID: PMC3771917 DOI: 10.1371/journal.pone.0074359] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 07/31/2013] [Indexed: 01/20/2023] Open
Abstract
Photoreceptor-specific nuclear receptor (PNR, NR2E3) is a key transcriptional regulator of human photoreceptor differentiation and maintenance. Mutations in the NR2E3-encoding gene cause various retinal degenerations, including Enhanced S-cone syndrome, retinitis pigmentosa, and Goldman-Favre disease. Although physiological ligands have not been identified, it is believed that binding of small molecule agonists, receptor desumoylation, and receptor heterodimerization may switch NR2E3 from a transcriptional repressor to an activator. While these features make NR2E3 a potential therapeutic target for the treatment of retinal diseases, there has been a clear lack of structural information for the receptor. Here, we report the crystal structure of the apo NR2E3 ligand binding domain (LBD) at 2.8 Å resolution. Apo NR2E3 functions as transcriptional repressor in cells and the structure of its LBD is in a dimeric auto-repressed conformation. In this conformation, the putative ligand binding pocket is filled with bulky hydrophobic residues and the activation-function-2 (AF2) helix occupies the canonical cofactor binding site. Mutations designed to disrupt either the AF2/cofactor-binding site interface or the dimer interface compromised the transcriptional repressor activity of this receptor. Together, these results reveal several conserved structural features shared by related orphan nuclear receptors, suggest that most disease-causing mutations affect the receptor's structural integrity, and allowed us to model a putative active conformation that can accommodate small ligands in its pocket.
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Affiliation(s)
- M. H. Eileen Tan
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
- Department of Obstetrics & Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - X. Edward Zhou
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
| | - Fen-Fen Soon
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
- Department of Obstetrics & Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Xiaodan Li
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
- Key Laboratory of Regenerative Biology, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China
| | - Jun Li
- Department of Obstetrics & Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Eu-Leong Yong
- Department of Obstetrics & Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Karsten Melcher
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
| | - H. Eric Xu
- Laboratory of Structural Sciences, Van Andel Research Institute, Grand Rapids, Michigan, United States of America
- Van Andel Research Institute/Shanghai Institute of Materia Medica Center, Chinese Academy of Sciences-Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
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West GM, Pascal BD, Ng LM, Soon FF, Melcher K, Xu HE, Chalmers MJ, Griffin PR. Protein conformation ensembles monitored by HDX reveal a structural rationale for abscisic acid signaling protein affinities and activities. Structure 2013; 21:229-35. [PMID: 23290725 DOI: 10.1016/j.str.2012.12.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2012] [Revised: 11/16/2012] [Accepted: 12/08/2012] [Indexed: 01/04/2023]
Abstract
Plants regulate growth and respond to environmental stress through abscisic acid (ABA) regulated pathways, and as such these pathways are of primary interest for biological and agricultural research. The ABA response is first perceived by the PYR/PYL/RCAR class of START protein receptors. These ABA activated receptors disrupt phosphatase inhibition of Snf1-related kinases (SnRKs), enabling kinase signaling. Here, insights into the structural mechanism of proteins in the ABA signaling pathway (the ABA receptor PYL2, HAB1 phosphatase, and two kinases, SnRK2.3 and 2.6) are discerned through hydrogen/deuterium exchange (HDX) mass spectrometry. HDX on the phosphatase in the presence of binding partners provides evidence for receptor-specific conformations involving the Trp385 "lock" that is necessary for signaling. Furthermore, kinase activity is linked to a more stable "closed" conformation. These solution-based studies complement the static crystal structures and provide a more detailed understanding of the ABA signaling pathway.
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Affiliation(s)
- Graham M West
- Department of Molecular Therapeutics, The Scripps Research Institute, Scripps Florida, Jupiter, FL 33458, USA
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Soon FF, Suino-Powell KM, Li J, Yong EL, Xu HE, Melcher K. Abscisic acid signaling: thermal stability shift assays as tool to analyze hormone perception and signal transduction. PLoS One 2012; 7:e47857. [PMID: 23112859 PMCID: PMC3480437 DOI: 10.1371/journal.pone.0047857] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 09/21/2012] [Indexed: 12/13/2022] Open
Abstract
Abscisic acid (ABA) is a plant hormone that plays important roles in growth and development. ABA is also the central regulator to protect plants against abiotic stresses, such as drought, high salinity, and adverse temperatures, and ABA signaling is therefore a promising biotechnological target for the generation of crops with increased stress resistance. Recently, a core signal transduction pathway has been established, in which ABA receptors, type 2C protein phosphatases, and AMPK-related protein kinases control the regulation of transcription factors, ion channels, and enzymes. Here we use a simple protein thermal stability shift assay to independently validate key aspects of this pathway and to demonstrate the usefulness of this technique to detect and characterize very weak (Kd ≥50 µM) interactions between receptors and physiological and synthetic agonists, to determine and analyze protein-protein interactions, and to screen small molecule inhibitors.
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Affiliation(s)
- Fen-Fen Soon
- Laboratory of Structural Sciences, Van Andel Research Institute, N.E., Grand Rapids, Michigan, United States of America
- Department of Obstetrics and Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Kelly M. Suino-Powell
- Laboratory of Structural Sciences, Van Andel Research Institute, N.E., Grand Rapids, Michigan, United States of America
| | - Jun Li
- Laboratory of Structural Sciences, Van Andel Research Institute, N.E., Grand Rapids, Michigan, United States of America
- Department of Obstetrics and Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Eu-Leong Yong
- Department of Obstetrics and Gynecology, National University Hospital, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - H. Eric Xu
- Laboratory of Structural Sciences, Van Andel Research Institute, N.E., Grand Rapids, Michigan, United States of America
- State Key Laboratory of Drug Research, VARI-SIMM Center, Center for Structure and Function of Drug Targets, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China
- * E-mail: (HEX); (KM)
| | - Karsten Melcher
- Laboratory of Structural Sciences, Van Andel Research Institute, N.E., Grand Rapids, Michigan, United States of America
- * E-mail: (HEX); (KM)
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6
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Zhou XE, Soon FF, Ng LM, Kovach A, Suino-Powell KM, Li J, Yong EL, Zhu JK, Xu HE, Melcher K. Catalytic mechanism and kinase interactions of ABA-signaling PP2C phosphatases. Plant Signal Behav 2012; 7:581-8. [PMID: 22516825 PMCID: PMC3419024 DOI: 10.4161/psb.19694] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Abscisic acid (ABA) is an essential hormone that controls plant growth, development and responses to abiotic stresses. ABA signaling is mediated by type 2C protein phosphatases (PP2Cs), including HAB1 and ABI2, which inhibit stress-activated SnRK2 kinases and whose activity is regulated by ABA and ABA receptors. Based on biochemical data and our previously determined crystal structures of ABI2 and the SnRK2.6-HAB1 complex, we present the catalytic mechanism of PP2C and provide new insight into PP2C-SnRK2 interactions and possible roles of other SnRK2 kinases in ABA signaling.
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Affiliation(s)
- X. Edward Zhou
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
| | - Fen-Fen Soon
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
- Department of Obstetrics & Gynecology; National University Hospital; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
| | - Ley-Moy Ng
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
- Department of Obstetrics & Gynecology; National University Hospital; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
| | - Amanda Kovach
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
| | - Kelly M. Suino-Powell
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
| | - Jun Li
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
- Department of Obstetrics & Gynecology; National University Hospital; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
| | - Eu-Leong Yong
- Department of Obstetrics & Gynecology; National University Hospital; Yong Loo Lin School of Medicine; National University of Singapore; Singapore
| | - Jian-Kang Zhu
- Department of Horticulture and Landscape Architecture; Purdue University; West Lafayette, IN USA
| | - H. Eric Xu
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
- VARI/SIMM Center; Center for Structure and Function of Drug Targets; Shanghai Institute of Material Medicine; Shanghai Institutes for Biological Sciences; Chinese Academy of Sciences; Shanghai, China
- Correspondence to: H. Eric Xu, and Karsten Melcher,
| | - Karsten Melcher
- Laboratory of Structural Sciences; Van Andel Research Institute; Grand Rapids, MI USA
- Correspondence to: H. Eric Xu, and Karsten Melcher,
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Soon FF, Ng LM, Zhou XE, West GM, Kovach A, Tan MHE, Suino-Powell KM, He Y, Xu Y, Chalmers MJ, Brunzelle JS, Zhang H, Yang H, Jiang H, Li J, Yong EL, Cutler S, Zhu JK, Griffin PR, Melcher K, Xu HE. Molecular mimicry regulates ABA signaling by SnRK2 kinases and PP2C phosphatases. Science 2011; 335:85-8. [PMID: 22116026 DOI: 10.1126/science.1215106] [Citation(s) in RCA: 343] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Abscisic acid (ABA) is an essential hormone for plants to survive environmental stresses. At the center of the ABA signaling network is a subfamily of type 2C protein phosphatases (PP2Cs), which form exclusive interactions with ABA receptors and subfamily 2 Snfl-related kinase (SnRK2s). Here, we report a SnRK2-PP2C complex structure, which reveals marked similarity in PP2C recognition by SnRK2 and ABA receptors. In the complex, the kinase activation loop docks into the active site of PP2C, while the conserved ABA-sensing tryptophan of PP2C inserts into the kinase catalytic cleft, thus mimicking receptor-PP2C interactions. These structural results provide a simple mechanism that directly couples ABA binding to SnRK2 kinase activation and highlight a new paradigm of kinase-phosphatase regulation through mutual packing of their catalytic sites.
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Affiliation(s)
- Fen-Fen Soon
- Laboratory of Structural Sciences, Van Andel Research Institute, 333 Bostwick Avenue NE, Grand Rapids, MI 49503, USA
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Melcher K, Ng LM, Zhou XE, Soon FF, Xu Y, Suino-Powell KM, Park SY, Weiner JJ, Fujii H, Chinnusamy V, Kovach A, Li J, Wang Y, Li J, Peterson FC, Jensen DR, Yong EL, Volkman BF, Cutler SR, Zhu JK, Xu HE. A gate-latch-lock mechanism for hormone signalling by abscisic acid receptors. Nature 2009. [PMID: 19898420 DOI: 10.1038/nature08613.a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Abscisic acid (ABA) is a ubiquitous hormone that regulates plant growth, development and responses to environmental stresses. Its action is mediated by the PYR/PYL/RCAR family of START proteins, but it remains unclear how these receptors bind ABA and, in turn, how hormone binding leads to inhibition of the downstream type 2C protein phosphatase (PP2C) effectors. Here we report crystal structures of apo and ABA-bound receptors as well as a ternary PYL2-ABA-PP2C complex. The apo receptors contain an open ligand-binding pocket flanked by a gate that closes in response to ABA by way of conformational changes in two highly conserved beta-loops that serve as a gate and latch. Moreover, ABA-induced closure of the gate creates a surface that enables the receptor to dock into and competitively inhibit the PP2C active site. A conserved tryptophan in the PP2C inserts directly between the gate and latch, which functions to further lock the receptor in a closed conformation. Together, our results identify a conserved gate-latch-lock mechanism underlying ABA signalling.
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Affiliation(s)
- Karsten Melcher
- Laboratory of Structural Sciences, Van Andel Research Institute, 333 Bostwick Avenue, N.E., Grand Rapids, Michigan 49503, USA
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